1. Field of the Invention
The present invention relates to a signal processing system and, more particularly, to a signal processing system for processing output signals from accumulating type photoelectric transducer elements such as an image pickup tube or a solid image-pickup element such as a CCD, BBD or CID.
2. Description of the Prior Art
Various conventional focus detecting systems for optical systems have been proposed. An increasing number of focus detecting systems have been proposed which utilize solid image-pickup elements such as the CCD, BBD or CID, the practicability of which has recently become notable. The characteristic feature of the image pickup tubes and solid image-pickup elements as described above resides in that extremely small photoelectric transducer elements are incorporated which produce time-serial electric signals of small picture elements of an image formed on an image pickup plane. Therefore, the image pickup tube and the solid image-pickup element allow subsequent time-serial processing of the signals and are therefore suitable for processing with electric circuitry, in contrast to conventional systems which have a plurality of usual photoelectric elements on which the image of an object is formed to produce photoelectric conversion signals of the image. Since the photoelectric transducer elements constituting the solid image-pickup elements, unlike the usual photoelectric transducer elements, serve to accumulate over a given period of time charge obtained by photoelectrically converting the energy of light incident thereon and to output time-serial signals, the area for each of these elements may be made very small so that the obtained time-serial signal train provides image signals of good resolution.
On the other hand, with a focus detecting system using an accumulating-type photoelectric transducer element, when the ambient temperature becomes high or the accumulating time becomes longer due to an increase in the intensity of incident light, the noise consisting mainly of dark current, that is, the signal fluctuation in each element (to be referred to as the sensitivity fluctuation hereinafter), becomes notable. For this reason, a focus defecting system using an accumulating-type photoelectric transducer element of the type described above is defective in that the detection precision is significantly degraded by the sensitivity fuctuation.